A gas turbine casing of a gas turbine accommodating interiorly components, such as a rotor and a nozzle diaphragm, is composed of a structure, which is divided into two halves by a horizontal plane and fastened by bolts in flange structures, in order to facilitate the installation and inspection of these components, and to prevent gas leakage during operation (see, for example, Patent Document 1 to be described below).
FIG. 4 is a schematic view showing a conventional gas turbine casing structure. In FIG. 4, its cross section in the axial direction of a bolt is illustrated.
As shown in FIG. 4, the gas turbine casing structure is divided into two halves, namely, an upper-half casing 100 and a lower-half casing 101. The upper-half casing 100 and the lower-half casing 101 are composed of shell sections 100a, 101a and flange sections 100b, 101b, respectively. The bonding between the upper-half casing 100 and the lower-half casing 101 is performed by fastening each bolt 102, each upper nut 103 and each lower nut 104 together.
That is, each flange of the gas turbine casing is divided into equal halves, i.e., the flange section 100b of the upper-half casing 100 and the flange section 101b of the lower-half casing 101. The flange sections 100b, 101b are provided with many bolt holes 100c, 101c. The bolt 102 is disposed in each of the bolt holes 100c, 101c, and fastened with the upper nut 103 and the lower nut 104.